We have begun to use the two-photon microscope at LAMMP to study FDA approved anticancer agents, Camptothecin derivatives, in single glioblastoma cells. To further characterize the cellular pharmacology of this new class of highly lipophilic camptothecins, we have studied the differential interactions of water-soluble versus highly lipophilic camptothecins (DB67) with human glioblastoma cells. Images obtained using two-photon microscopy of glioblastoma cells show a clear correlation with between drug lipophilicity and drug fluorescence levels achieved in the cells. Very high levels of staining were achieved with highly lipophilic DB67, and levels fell off with decreasing drug lipophilicity. Our data indicate that DB67 can extensively interact with the glioblastoma cells, and other cell lines are now being studied as well. Future studies will involve characterizing camptothecin interactions with a variety of cancer cells and tumor spheroids using the two-photon micro sco py technology. It will be interesting to compare how HSA modulates the cellular accumulation of a protein-interactive drug such as camptothecin versus a drug with reduced interactions such as the new experimental analog DB-67.